/Engine/Plugins/Experimental/Mutable/Source/MutableRuntime/Public/MuR/ExtensionDataStreamer.h
The newExtensionDatashould be completely independent of the sourceExtensionData, such that if the source instance is deleted, the new instance should still be valid.
[ExtensionDataPtr](API\Plugins\MutableRuntime\MuR\ExtensionDataPtr) CloneExtensionData ( const [ExtensionDataPtrConst](API\Plugins\MutableRuntime\MuR\ExtensionDataPtrConst) & Source )